# CVE-2026-43027: Linux Kernel use-after-free in Netfilter nf_conntrack_helper

Source: https://junglewise.ai/threats/cve-2026-43027-linux-kernel-use-after-free-in-netfilter-nf-conntrack-helper  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-01. Updated: 2026-07-14  
License: CC BY 4.0 with a link back

CVE-2026-43027 · Severity: high · CVSS 7.8 · Published 2026-05-01

A vulnerability exists in the Linux kernel's networking subsystem (Netfilter) that could allow a local user to crash the system or potentially execute unauthorized code. The issue occurs when the system fails to properly clean up internal tracking data when a network helper component is removed. This can lead to a 'use-after-free' condition, impacting the stability and security of servers and embedded devices using affected versions of the Linux kernel.

Technologies: [Linux Kernel](https://junglewise.ai/threats/technologies/kernel), [Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP](https://junglewise.ai/threats/technologies/simatic-s7-1500-cpu-1518-4-pn-dp-mfp), [Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP](https://junglewise.ai/threats/technologies/simatic-s7-1500-cpu-1518f-4-pn-dp-mfp). Vendors: [Linux](https://junglewise.ai/threats/vendors/linux), [Siemens](https://junglewise.ai/threats/vendors/siemens).

## Quick answers

**Is CVE-2026-43027 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-43027 being exploited in the wild.

**How severe is CVE-2026-43027?** High severity, with a CVSS score of 7.8, published 1 May 2026.

**Which products and versions are affected?** Linux Kernel Fixed in various stable branches including 5.10.y, 5.15.y, 6.1.y, 6.6.y, 6.8.y; Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP V3.1.5, V3.1.6; Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP V3.1.5, V3.1.6.

**Is there a fix for CVE-2026-43027?** A patch was published on 2026-04-11: Initial patches applied to stable kernel trees. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-43027 attacked?** It is attacked with local access, in an operating system.

**Am I affected by CVE-2026-43027?** Check whether you run Linux Kernel, Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP or Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A use-after-free vulnerability exists in net/netfilter/nf_conntrack_helper.c. The function nf_conntrack_helper_unregister() incorrectly passed a NULL pointer to nf_ct_expect_iterate_destroy() instead of the actual helper pointer. Consequently, expectations associated with the helper were not destroyed during unregistration. When the helper object was subsequently freed by nfnl_cthelper_del(), remaining expectations maintained a dangling pointer to the freed memory. Subsequent access via expectation dumps or packet-driven conntrack initialization triggers the use-after-free. This can be exploited by a local user to cause a kernel panic or potentially achieve arbitrary code execution. Patches have been released for multiple stable Linux kernel branches.

## Affected products

- Linux Linux Kernel Fixed in various stable branches including 5.10.y, 5.15.y, 6.1.y, 6.6.y, 6.8.y
- Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP V3.1.5, V3.1.6
- Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP V3.1.5, V3.1.6

## Timeline

- 2026-05-01: disclosed
- 2026-04-11: patched: Initial patches applied to stable kernel trees.

## References

- [https://git.kernel.org/stable/c/2c16e4d64dd91227742dfe196a3e7b0568bef65a](https://git.kernel.org/stable/c/2c16e4d64dd91227742dfe196a3e7b0568bef65a)
- [https://git.kernel.org/stable/c/2cf2737c85a2ba2b52024dafe68ffad2676f97be](https://git.kernel.org/stable/c/2cf2737c85a2ba2b52024dafe68ffad2676f97be)
- [https://git.kernel.org/stable/c/504ba4168466c91210c45acdc332479cfd5f2da6](https://git.kernel.org/stable/c/504ba4168466c91210c45acdc332479cfd5f2da6)
- [https://git.kernel.org/stable/c/5cf28d5c8dcbbe8af6d3b145babe491906d7bad1](https://git.kernel.org/stable/c/5cf28d5c8dcbbe8af6d3b145babe491906d7bad1)
- [https://git.kernel.org/stable/c/620f3d14c1ef51d425060a3056ad8dbae8f998a3](https://git.kernel.org/stable/c/620f3d14c1ef51d425060a3056ad8dbae8f998a3)
- [https://git.kernel.org/stable/c/90bd7e8501349db3006d21fbc09df9ffcb172965](https://git.kernel.org/stable/c/90bd7e8501349db3006d21fbc09df9ffcb172965)
- [https://git.kernel.org/stable/c/a242a9ae58aa46ff7dae51ce64150a93957abe65](https://git.kernel.org/stable/c/a242a9ae58aa46ff7dae51ce64150a93957abe65)

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